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Rocks Chapter 4-1 The Rock Cycle The Rock Cycle Rock – mixture of minerals, glass or organic matter. Granite: igneous rock Mica Plagioclase Orthoclase Horneblend quartz Rock Cycle Older rocks are recycled to make younger rocks. Various processes that alter the rocks; Melting Temperature and pressure Weathering, erosion and deposition Three basic rock groups are formed: Igneous – melting and cooling Sedimentary – weathering, erosion and deposition • Cementing and compacting Metamorphic – temperature and pressure Igneous Rocks Formed from molten material in earth’s crust that emerges or remains in earth’s crust. Magma – liquid rock UNDER crust Lava – liquid rock ON crust Causes of extreme heat in Earth Pressure Heat from earth’s interior Radioactive elements Two kinds of igneous rocks Intrusive igneous rocks – Cooled slowly Texture – coarse grained - time for large crystal growth Found in surface of earth after weathering Pegmatite Extremely large crystals Long time for crystal growth Intrusive sites Gabbro Plagioclase feldspar Pyroxene Diorite Salt and pepper rock Granite Hornblende – black White Plagioclase – white/gray Extrusive Igneous Rocks Cools near earth’s surface Cools quickly Texture – fine grained Rhyolite Feldspar Quartz Biotite mica Fine texture Basalt Iron rich Pyroxene Plagioclase Olivine Fine texture Quick cooled Obsidian Volcanic glass Texture – glassy SiO2 Conchoidal fracture Pumice Frothy or Glassy threads Silica based Gases emitted from lava at explosion cause strings that make threads So light it floats on water Scoria Large holes made by gas escaping from lava Volcanic cinders Lava rock Basaltic – darker than pumice Classification of Igneous Rocks Igneous rock classified by composition Basalt – dense, heavy, dark colored - rich in Fe and Mg - lava quick moving - ocean bottoms Granitic – light colored, lower density - magma thick contains Si and O2 - continental plates - contains great deal of gases (explosive) Andesite – between basalt and granite - violent eruptions Igneous rocks can be classified by; Composition Basalt – ferromagnesium – Fe and Mg Granite – potassium and silicates SiO2 Texture: Large crystals Small/no crystals Place of cooling: Intrusive extrusive Textbook page 92 answer in notebook Self Check 1,2, 3, 4, Applying skills
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